1. Field of the Invention
The present invention relates to a method of estimating loads imposed on a structural body based on measured strains or flexures of the structural body that are caused by applied loads.
2. Prior Art
There has been known a method of estimating a load imposed on a structural body by attaching a strain measuring device such as a strain gage to the structural body, directly measuring a strain of the structural body where the strain gage is applied, determining a stress from the measured strain, and estimating a load acting on the structural body from the determined stress.
When an axial force is applied to a column having a simple shape, the following equation is satisfied: EQU E=.sigma./.epsilon.=(P/A)/(.lambda./1)
where E represents the modulus of longitudinal elasticity of the load, (.sigma. the simple vertical stress of the rod, .epsilon. the longitudinal strain of the rod, P the axial load imposed on the rod, A the cross-sectional area of the rod, .lambda. the extension or compression of the rod, and 1 the original length of the rod.
However, actual structural bodies do not have a uniform cross-sectional shape. Loads are applied to actual structural bodies in complex directions and at plural points thereon. Therefore, although strains of actual structural bodies caused by loads applied thereto can be measured, it is almost impossible to convert the measured strains into the applied loads.
One solution is to carry out a computer simulation process on a structural body rather than measuring developed strains of the structural body. It is, however, not reliable enough to estimate applied loads through calculations according to the computer simulation process because calculated results tend to differ widely depending on how the structural body is modeled and it is difficult to assume loading conditions. In addition, since the computer simulation process is supposed to estimate loads while the structural body is being designed, it imposes limitations on efforts to determine loads which will, be applied when the structural body is in actual use.
It would be highly beneficial for aircraft design and safety management purposes if the magnitude of loads applied to various parts of an aircraft main wing can be determined in actual flight.
Specifically, even if a number of strain gages are attached to various parts of an aircraft main wing, they produce only signals indicative of strains of those parts, providing a basis to determine whether the strains are less than allowable levels or not. The strain gages alone fail to determine the magnitude of loads applied to the various parts of the aircraft main wing.